What is a tosylate group?
A tosylate is the anion of tosylic acid.
This is tosylic acid (or p-toluenesulfonic acid):
so the conjugate base is a tosylate. It is toluene (methylbenzene) with a sulfonate group attached on the 4-position.
Related are tosyl leaving groups because they are large and they tend to have a low
A common "tosyl" compound is tosyl chloride.